Floating mooring arrangement

ABSTRACT

A floating mooring arrangement, for example for transferring liquified natural gas between the sea bottom and a ship, comprises a tower resting on the sea bottom, and a pair of concentric annular members surrounding the tower and floating on the surface of the water. The outer of these has a buoyant arm rigidly connected thereto, to which the ship is connected. The inner of these is secured by anchors and anchor chains. Conduits extend from the sea bottom up through the tower and from a swivel at the top of the tower to pipes on the outer annular member, and thence to the ship. Clearance between the tower and the annular members is such that the latter cannot touch the tower within the range of movement afforded by the anchor chains.

United States Patent Van der Gaag l l Sept. 30, 1975 1 FLOATING MOORINGARRANGEMENT [75] Inventor: Cornelis Van der Gaag. Delft, -Y"("" Bhx a vAss/stun! L.\'un11nerSherman D. Basmger Netherlands Altornqv, Agent, orlawn-Young & Thompson [73] Assignee: N.V. lndustrieele HandelscombinatieHolland, Rotterdam, Netherlands ABSTRACT [22] Filed: 1974 A floatingmooring arrangement, for example for [2]] Appl. No: 433,244 transferringliquified natural gas between the sea bottom and a ship, comprises atower resting on the sea A r P D bottom, and a pair of concentricannular members Forelgn pp canon am surrounding the tower and floatingon the surface of Jan. 19. 1973 Netherlands 7300820 h water Th Outer fthese h a buoyant arm i idly connected thereto, to which the ship isconnected. [52] US. Cl. 1. 114/230; 9/8 P The inner f these is securedby anchors and unchor 3633 21/00; 3633 21/52 chains. Conduits extendfrom the sea bottom up [58] Field of Search l l4/0.5 F, 230; 9/8 throughthe tower and from a swivel at the top of the 61/465 46 tower to pipeson the outer annular member, and thence to the ship. Clearance betweenthe tower and References Clled the annular members is such that thelatter cannot UNITED STATES PATENTS touch the tower within the range ofmovement af- 3.366.982 2/1968 Sutton 9/8 P forded y the anchor Chains-3,595 l96 7/197] Riffeser 9/8 P 3,668.875 6/1972 Sander et .11 114/230 2Clams 2 Draw'ng F'gum US. Patent 'Sept. 30,1975 3,908,576

FLOATING MOORING ARRANGEMENT This invention relates to a floatingmooring arrangement comprising a first part which by means of anchors isheld in place and a second part which is rotatable relative to the firstpart about an essentially vertical shaft and which comprises means forsecuring a ship thereto, and furthermore one or more conduits extendingfrom the seabottom upwards to a rotatable connection and from there tothe rotatable part of the arrangment. Mooring arrangements of this kindare generally known in many embodiments. The anchored arrangement ismovable to a cetain extent and the rotatable part can be rotated throughan angle of 360 in order to afford the ship that has made fast to thearrangement the opportunity to adapt itself to the wash of the waves,the current and the direction of the wind.

In case a liquefied natural gas must be conveyed via such a mooringarrangement the known mooring arrangement is generally not serviceableanymore. The conduits extending from the arrangement to the bottomshould be capable of adapting themselves to the movements of thearrangement. However, these conduits become rigid on account ofdeposition of ice be cause the liquified gas is sub-cooled (l60C.)

The invention aims at providing a mooring arrangement with which it ispossible to handle sub-cooled media. This object is arrived at accordingto the invention in that the arrangement comprises a ring, that theconduits extend upwards via a tower placed on the seabottom and from thetower to the rotatable part of the ring in the form of hoses rarticulated pipe connections and that the ring has so much interiorspace relative to the tower that said ring will not touch the towerwithin the range of movement offered by the anchor chains.

The submerged conduit section on which deposition of ice may take placeis now arranged in or at the stationary tower which is located withinthe annular part of the arrangement, does not take up anchor forces andalso does not come into contact with the arrangement. The onlyconnection between tower and arrangement is constituted by the hoses orarticulated pipe connections extending from the rotatable tower top tothe rotatable part of the arrangement. These connections are visible anddeposition of ice can therefore be ascertained and combatted, forinstance by heating the outside of this comparatively short stretch.With a simple heating coil laid along the hose or wrapped around it itis possible to counteract a deposition of ice thus maintaining themovability of said connection.

According to the invention the rotatable part of the arrangement mayfurthermore comprise a ring and to this ring an arm having buoyancy maybe tangentially connected so that a ship to be handled may make fast tosaid arm. As a result the movements of the arrangement are determined toa considerable extent by the movements of the ship, the more so becausethe arrangement and the mooring arm itself have only a small surface atthe water level. The movements of the arrangement relative to the towerare therefore more limited then would be the case if the arm did notform one rigid unit with the rotatable ring of the buoy. Naturally therotatable ring is completely supported both axially and radially.

The annular shape protects the tower against the action of the waves.

It is to be noted that the application of a tower is known in itselffrom the US. Pat. No. 2,699,321 which shows a mooring arrangementmounted to swing about the tower.

The invention will now be further elucidated with reference to thedrawings.

FIG. 1 shows a top plan view of the mooring arrangement, and

FIG. 2 a side view of the same arrangement.

The arrangement shown in the drawings comprises a tower 1 which has beenplaced on the seabottom 2 and to which conduits 3 are connected whichextend on the seabottom 2. Said conduits extend upwards through thetower (not shown). In the top of the tower there is fitted a rotatablehead 4 to which hoses 5 are connected. Said hoses are connected to aconnecting head 6 from which conduits extend, in a manner not shown, toconnecting points for the ship to be handled as shown for instance atreference numeral 8.

The buoy comprises an annular body 9 which is secured with anchor cablesor chains 10 and about which a ring 11 is rotatably arranged, on whichthe aforementioned connecting head 6 is fitted and to which furthermorean arm 12 is rigidly fastened. Conduits extend through said arm to theconnecting point 8 which is provided with the necessary means such asfenders 13 and bollards 14 for anchoring a ship 7.

The space within the body 9 around the tower is so large that themovements which the body 9 may carry out under the influence ofprevailing conditions do not result in a load on the tower. This towermay stand on the seabottom so that in the event of a collision, forexample in the event of an anchor chain being ruptured, damage betweenbuoy and tower need not always be serious.

In the case of subcooled media being pumped deposition of ice will takeplace mainly in that part of the conduit that is below the water level.In the part above the water checking and removal is easily carried out.

It is to be noted that the mooring arrangement may also be designed suchthat the part to which the anchor chains are fastened has no buoyancy ofits own and is mounted in the rotatable part which does have buoyancy.The non-floating part may then be a frame supported in a bearing collarof the floating part.

I claim:

1. Floating mooring arrangement comprising a first annular part held inplace by anchors and anchor chains, a second annular part which isrotatable relative to the first part about a vertical axis and which hasmeans thereon for mooring a ship thereto and further comprising a towerplaced on the sea bottom and extending upward through said first annularpart, conduits'extending from the sea bottom upward via the tower, theupper end of said conduits through a swivel and flexible conduits beingconnected to pipes on the second annular part, said annular parts havinginner diameters such that within the range of movability allowed by theanchor chains to the first annular part, said parts cannot touch thetower, said first and second annular parts riding on the surface of thewater and being vertically movable relative to the tower.

2. An arrangement as claimed in claim 1, said second annular partcomprising a ring with an arm having buoyancy tangentially connectedthereto.

1. Floating mooring arrangement comprising a first annular part held inplace by anchors and anchor chains, a second annular part which isrotatable relative to the first part about a vertical axis and which hasmeans thereon for mooring a ship thereto and further comprising a towerplaced on the sea bottom and extending upward through said first annularpart, conduits extending from the sea bottom upward via the tower, theupper end of said conduits through a swivel and flexible conduits beingconnected to pipes on the second annular part, said annular parts havinginner diameters such that within the range of movability allowed by theanchor chains to the first annular part, said parts cannot touch thetower, said first and second annular parts riding on the surface of thewater and being vertically movable relative to the tower.
 2. Anarrangement as claimed in claim 1, said second annular part comprising aring with an arm having buoyancy tangentially connected thereto.